A sediment core taken near the discharge point of a wastewater treatment plant into the Cutler Reservoir wetland (northern Utah, USA).

To take a core, a weighted cylinder with a plastic insert (shown) is dropped to the bottom of the lake, brought back to the surface and removed from the device.

This core was taken to measure sediment oxygen demand (SOD) and phosphorus regeneration. The oxygen demand from the sediments contributes to anoxia in the water column, and the nutrient regeneration fuels additional phytoplankton (algae) growth in the water column. This "internal loading" of nutrients is a serious problem contributing to eutrophication of polluted waters.